1. Field of the Invention
This invention relates to storage systems and more particularly relates to redundant identification of a storage medium format.
2. Description of the Related Art
Common storage media and storage systems include various hardware and media configurations and formats. As technology progresses, storage densities improve, error rates are reduced, and data reliability is increased. These advances are typically implemented in successive versions, revisions, or generations of storage systems or storage media products.
For example, the 3592 Enterprise™ tape storage system offered by International Business Machines® (“IBM”) is just one of many members of a family of storage system products. Changes may be implemented in various revisions and generations even among individual models. For example, the model 3592 Enterprise™ tape storage system includes a First Generation (“G1”), and a Second Generation (“G2”). In this example, the read and write format of G1 is different from the read and write format of G2.
Since various media formats may exist, common storage media often include identifiers for informing devices that may interface with the storage media of which format is being employed. For example, in the operation diagram depicted in FIG. 1, a tape storage medium 102 may include a Format Identification Data Set (“FID”) 106 for identifying the format of the user data 108 written on the tape 102.
A typical tape cartridge may include a Cartridge Memory (“CM”) for storing the FID and other information used by a tape drive for reading data stored on the tape cartridge. However, in certain situations the CM may not be available. For example, the data in the CM may be corrupted, the drive may be unable to read the CM, or the like. In response to this issue, tape drives often write a backup version of the FID at the beginning of the tape, so that the drive can continue to function even if the CM is unavailable.
If the FID is unavailable, the drive is unable to determine the layout information required to read and write the tape. Layout information may include the track pitch, encryption data, compression data, and the like. If this information is unavailable, the tape drive is unable to read or write data to the tape cartridge.
In the example depicted in FIG. 1, a typical tape storage system includes a tape data storage medium 102. The tape 102 typically has a predetermined start point 104 of a user area. In a common system, the FID 106 is located at the start point 104. User data 108 is then typically written on the portion of the tape 102 following the FID 106. However, certain problems may arise when tapes 102 configured for different generations of storage equipment are employed. For example, an error may occur if a G2 tape is loaded into a G1 tape drive. Although the tape 102 may be physically compatible with the drive, the formats may be incompatible.
In response to these issues, many manufacturers make successive versions backwards compatible with prior versions of the same model. For example, the G2 version of the model 3592 Enterprise™ tape storage system may also be compatible with the G1 version. In such an example, the G2 drive may still be able to read and write data on a G1 format tape 102.
In the example depicted in FIG. 1, the model 3592 Enterprise™ tape drive reads the FID 106 at the starting point 104 of the user area on the tape 102. Typically the FID 106 is written in G1 format so that both G1 and G2 devices can use the tape 102. If FID 106 indicates that the tape 102 is in the G2 format, the drive must stop the tape 102 and change internal read and write components and drivers to be compatible with the G2 format. Only then can the drive continue to read the user data 108 on the tape 102.
This problem is exacerbated with certain operations. For example, when a typical drive rewinds a tape 102, the drive usually reads the FID 106. In such an example, each time the tape 102 is rewound, the drive must change to G1 configuration to read the FID 106 and then change back to G2 configuration to continue reading the user data 108. Each of these changes requires the tape 102 to stop and internal configuration to change. These operations typically waste read and write time. Additionally, in systems where mechanical components are required to change in order to change configurations, excessive wear and tear may occur.